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From the Journal of Infection and Public Health website:
Dissemination of aerosol and splatter during ultrasonic scaling: A pilot study
Dentists and dental personnel operate in the highly contaminated environment of the oral cavity. Routine dental procedures such as tooth preparation and ultrasonic scaling and a simple manoeuvre such as the use of an air water syringe produce aerosol and splatter, which poses a potential risk to the clinician, the dental personnel and the immunocompromised patient. The composition of aerosol differs from patient to patient and according to the nature of procedure, such as tooth preparation and scaling.
The oropharynx is the primary site of colonization of potential respiratory pathogens and oral biofilm acts as a reservoir for these pathogens . Reports indicate that the ultrasonic scaler is the greatest producer of aerosol and splatter . Studies also indicate that the cavitation effect during piezosurgical procedures produces a significant amount of aerosol by the coolant fluid in the process of washing away blood and providing optimal visibility to the operating field .
An aerosol can be defined as, “A suspension of solid or liquid particles in a gas”. The particle size of an aerosol is less than 50 μm. Splatter can be defined as airborne particles larger than 50 μm . The solid and liquid phases of an aerosol are comprised bacteria, blood elements, viruses, and organic particles of tissue, tooth, saliva and debris . The amount of aerosol contamination depends on the quality of saliva, nasal and throat secretions, blood, dental plaque, and the presence or absence of any dental infection. In addition to this, dental unit water lines contribute to aerosol contamination due to narrow bore water lines, water stagnation, heating of the dental chair unit, anti-retraction valve failure and contamination of reservoir bottles. Dental unit water lines also have a hydrophobic polymeric plastic tubing made of polyvinyl chloride and polyurethane that leads to the formation of biofilm, which releases a high number of planktonic organisms within 8 h, followed by the formation of communities of microcolonies that are protected by an extracellular amorphous matrix for six days .
There is an increased prevalence of respiratory infections among dentists, the symptoms of which are related to the highly contaminated breathing zone in the dental operatory. Aerosols remain in the air for a long time even after the completion of the dental procedure and have the potential risk of entering the respiratory passages. Splatter evaporates, leaving smaller particles called droplet nuclei, which can carry bacteria and viruses and transmit various diseases such as SARS and tuberculosis . Following a rise in communicable diseases, infection control has become an essential part of the dental operatory and also forms an integral part of the curricula of dental schools. Performing periodic checks on environmental contamination is recommended to improve the quality of the environment in the dental operatory .
In this study, we aimed to evaluate the contamination distance, contamination amount and contamination duration of aerosols produced during ultrasonic scaling.
Materials and methods
The study was performed on a mannequin fitted with phantom jaws on a dental chair, set in the reclining position simulating the dental operatory. From the head rest, adhesive tapes were set up in six directions corresponding to the 12, 2, 4, 6, 8 and 10 o’clock positions up to a distance of 5 ft. Grade no. 1 qualitative white filter paper discs made from cotton cellulose fibres of diameter 9.0 cm and thickness of 0.2 mm were used for the study. These discs retain large crystalline particles and gelatinous precipitates. They have a smooth surface and normal hardness. The filter paper discs were placed on these adhesive tapes at every 1 ft distance (Fig. 1). They were also placed on the head, chest, arms and inner surface of the face mask of the operator and of the assistant. Each filter paper disc was assigned a code depending on the position, distance and duration.
Fluorescein [resorcinol phthalein (C20H12O5), melting point – 320 °C, molecular weight – 332.31] is an orange-red odourless powder. This dye is commonly used in microscopy, in a type of dye laser as the gain medium, in forensics and serology to detect latent blood stains and also in dye tracing. In the current study, fluorescein dye was procured from Loba Chemie Laboratory Reagents and Fine Chemicals and used in the coolant supplying the ultrasonic scaler unit. 1 g of fluorescein dye was added to 1 l of distilled water and filtered. This was used in the reservoir supplying the ultrasonic scaler unit (Figure 2, Figure 3). Mock scaling was done for 15 min using an auto tuned magnetostrictive ultrasonic scaler operating at 25,000 Hz set at high power with the simultaneous use of a conventional low volume saliva ejector (Fig. 4) Immediately following scaling, the filter paper discs were replaced with new ones. Filter paper discs were replaced every 30 min for a total duration of 90 min.
The contamination amount was measured using a transparent grid containing 1 cm2 squares. The grid was placed over the filter paper disc and area of contamination was measured by counting the number of contaminated 1 cm2squares (Fig. 5). If a square had at least one yellow area, it was counted as contaminated.
Contamination area and distance (Figs. 6 and 7, Tables 1–4)
Immediately following scaling, contamination was found at 1 ft in the 4, 6, 8 and 10 o’clock positions, at 2 ft in the 4, 8 and 10 o’clock positions and at 4 ft in the 2 o’clock position. Maximum contamination was found at 1 ft in the 4 o’clock position followed by 1 ft in the 6 o’clock position, and 1 ft in the 12 o’clock position.
Table 1. Distance and surface area of contamination immediately after scaling.
|Position||Surface area (cm2)|
|1 ft||2 ft||3 ft||4 ft||5 ft|
Table 2. Distance and surface area of contamination 30 min after scaling.
|Position||Surface area (cm2)|
|1 ft||2 ft||3 ft||4 ft||5 ft|
Table 3. Contamination areas on right handed operator immediately after scaling.
|Part on operator||Surface area of contamination (cm2)|
|Inside of face mask||4|
Table 4. Contamination areas on right handed assistant immediately after scaling.
|Part on assistant||Surface area of contamination (cm2)|
|Inside of face mask||1|
Contamination was also found on the head, chest and inner surface of the face mask of the operator and of the assistant. Maximum contamination was found on the right arm of the operator and left arm of the assistant.
30 min after scaling, contamination was found at 1 ft in the 4, 6, 8 and 10 o’clock positions. Maximum contamination was seen at 1 ft in the 4 o’clock position followed by 1 ft in the 6 o’clock position, and 1 ft in the 10 o’clock position.
The aerosol cloud was found to remain in the air up to 30 min after scaling as there was no evidence of contamination of filter paper discs 60 min after scaling.
Ultrasonic scaling produces the greatest amount of aerosol and splatter, which can be disseminated to a considerable distance from the operating site. An in vitro study showed that an ultrasonic scaler without a coolant still produced a significant amount of aerosol and splatter with small amount of liquid placed in the operating site to simulate blood and saliva .
Any dental procedure results in some amount of mucosal damage, which is practically unavoidable. Hence, it is very important to treat every patient as a potentially infective patient in our everyday practice. With the emergence of newer periodontopathogens and resistant established pathogens, it becomes mandatory to follow universal barrier techniques.
In our study, maximum aerosol contamination was found in the assistant zone followed by the operator's zone. The arms, chest and inner surface of the face mask of both the operator and the assistant were found to be contaminated. Previous studies also reported similar results . A recent study also demonstrated that areas around the nose and inner corner of the eyes show a significantly higher rate of contamination .
Face masks should be snugly fitting as contaminants can bypass the filtering effect of these masks. A relationship between pore size of the surgical mask and bacterial filtration efficiency has been studied. The mask with the smallest pore size has been shown to have the maximum bacterial filtration efficiency. Studies have shown that fit of the mask, proper positioning of the mask, movement by the wearer, length of facial hair and voice level while speaking all have a direct bearing on bacterial filtration efficiency .
The aerosol cloud remained in the operatory 30 min following the procedure in the present study. An earlier study reported that the peak of aerosol concentration dissipates within 10–30 min with scaling procedures . Therefore, it is recommended that the operator should not remove the protective barrier immediately after the procedure to reduce the risk of contact with airborne contaminants. There is also a potential risk for airborne contaminants to enter the ventilation system and spread infection. High efficiency particulate air (HEPA) filters and UV chambers in the ventilation system can minimize the risk of air contamination . Air disinfection with a lamp emitting ultra-violet radiation 250–265 nm shows very high fungicidal, virucidal and bactericidal action through destruction of DNA chains and protein denaturation . However, these techniques are expensive. Cost-effective methods such as the use of a high volume evacuator with a large bore evacuator tip should be advocated for during ultrasonic scaling. The large bore tip with a diameter of 8 mm or more can remove air at the rate of 100 cubic feet per minute. This reduces aerosol and splatter by 93–96% . A low volume saliva ejector that we used removes the water collecting in the floor of the mouth rather than removing the air. Therefore, it may not be a very efficient tool in reducing the aerosol cloud.
In general, the dental operatory should be seen as an operation theatre rather than an office to minimize the risk of cross infection.
Our study demonstrated the quantitative assessment of aerosol contamination during ultrasonic scaling. However, air quality assessment could not be demonstrated as the study was conducted on a simulated model of the dental operatory. It was also assumed in our study that the aerosols are uniformly distributed in the air; hence, only a particular area of the dental operatory was considered as a sample for estimation of contamination. However, this pilot study provides an impetus to conduct clinical studies on air quality assessment in the dental operatory and adopt suitable measures to improve quality of air breathed and prevent occupational health hazards. The risk of dental aerosols can be minimized by following simple, inexpensive precautions such as adequate ventilation in the operatory; personal barrier techniques such as disposable gloves, face masks and protective eye wear; use of high volume evacuators; disinfection of dental unit water lines by chemical and non-chemical approaches; use of focused spray ultrasonic inserts; and pre-procedural rinsing. Additionally, the importance of personal hygiene for dental personnel before and after work should be emphasized to control bacterial colonization and spread of hospital bacteria in the community.